PROVIDED. This application proposes the identification and preclinical development of novel small molecule antagonists of the Vif protein of HIV-1. Apobec 3G is a cytidine deaminase which potently antagonizes HIV-1 infection. To counteract this cellular restriction, primate lentiviruses such as HIV-1 have evolved a Vif protein, the function of which is to target apobec for proteasomal destruction. Viruses containing mutations in Vif are severely compromised in vitro and in vivo. Therefore, Vif is a critical, yet unrealized, therapeutic target. Through institutional support and a grant from Howard Hughes Medical Institute, UMass Medical School (UMMS) has recently established a high throughput inhibitor screening facility and the identification of compounds that block the action of HIV-1 Vif was prioritized. As a result of this initial screening, two lead compounds that block Vif-mediated apobec destruction have been identified. These compounds inhibit HIV- 1 replication only in the presence of apobec and as such, are bona fide Vif inhibitors. This provides proof-ofprinciple that novel inhibitors of the HIV-1 Vif protein can be identified. This program project application will combine individuals with expertise in drug discovery, HIV-1 virology and SIV immunopathogenesis for the preclinical development of novel antagonists of HIV-1 Vif. The program project comprises: Project 1, T. Rana, Ph.D., UMMS, Vif antagonists: lead inhibitor identification and SAR analysis. Project 2, M. Stevenson, Ph.D., UMMS, Vif antagonists: evaluation of antiviral activity and mechanism of action in vitro. Mechanisms of inhibitor resistance in vitro and in vivo. Project 3, K. Mansfield, D.V.M., Harvard and NEPRC, Vif-antagonists: small animal PK and toxicity profiling, evaluation in chronic SIV infection model and in model of SIV-induced encephalitis. Core A, Administrative Core Core B, B. Beer, Ph.D., Southern Research Institute, Vif-antagonists: inhibitor sensitivity of clinical HIV-1 isolates, and plasma SIV RNA assays in treated monkeys. Through this program project, we propose the preclinical development of a new class of compounds that antagonize HIV-1 and SIV Vif and which will be used to assess the consequences of Vif antagonism in lymphoid and CNS reservoirs of viral replication in vivo.